Anybody have any links or pointers to controls/controllers for setups
using 2 (or more) boilers to supply larger-than-usual loads? I recall
someone on this list did such a thing for a church he's involved with.
I'm looking at an installation which has a couple of Baxi Solo 2s but no
integration (just a user-unfriendly array of switches and valves to
operate to bring one or both into service as required).

I'm inclined to just have one boiler on load all the time and an outside
thermostat to bring the second in during cold weather (sort of weather
compensation scheme) but it would be interesting to know what's available
(and how much it would cost) to do the job 'properly'.

--
John Stumbles -- http://yaph.co.uk

I'd rather have a full bottle in front of me
Than a full-frontal lobotomy

In message , YAPH
writes
Anybody have any links or pointers to controls/controllers for setups
using 2 (or more) boilers to supply larger-than-usual loads? I recall
someone on this list did such a thing for a church he's involved with.
I'm looking at an installation which has a couple of Baxi Solo 2s but no
integration (just a user-unfriendly array of switches and valves to
operate to bring one or both into service as required).

I'm inclined to just have one boiler on load all the time and an outside
thermostat to bring the second in during cold weather (sort of weather
compensation scheme) but it would be interesting to know what's available
(and how much it would cost) to do the job 'properly'.


I had a customer with such a beast controlling two suprimas

Intuition told me to keep them at arms length and not get too involved,
but I can give you their number


--
geoff

On 28 Apr 2011 22:51:03 GMT Yaph wrote :
Anybody have any links or pointers to controls/controllers for setups
using 2 (or more) boilers to supply larger-than-usual loads? I recall
someone on this list did such a thing for a church he's involved with.

Yes, that was me. We did it the cheap and cheerful way as a proper
sequencer would have cost four figures, not justified, and the ones I
looked at were more suited for a Mon-Fri 8-6 heating regime rather than
the varied times and temps you have with church heating (we had 18C for
services, 19C for longer sitting still meetings, and 15C for flower
arrangers and cleaning).

I've just dug out an old pipework schematic and uploaded it as
http://www.greentram.com/tony/TwinKestonBoiler.pdf

I haven't got a circuit diagram for the controls unfortunately, but
basically a CM67 master controller goes went a two-way switch to the
boiler A and boiler B call for heat terminals. This switch set the lead
boiler. Between the switch L1 and L2 terminals were two thermostats in
series - if both are closed the second boiler runs too. The first was a
second CM67 set around 0.5C lower than the main one, also (for our usage)
time/temp set to kill the second boiler around 20-30 minutes before the
end of a heating session, the second a pipe stat at the bottom of the
boiler shunt pipe which opened if the return temp rises above (depending
on setting) 55-60C - which it would if the fan convectors were running at
low speed or not all on.

For someone with the electronic knowledge to make a controller, an
alternative control algorithm might be to pull in the second boiler if the
first has been running for 10-15 minutes and to hold it off for a similar
period when the call for heat stops. From cold this would give a slower
initial warm up but once the building was at a temp where you needed one
boiler (or less) the second would never get called. Might run into
problems though if the first boiler modulates down to 80% (being all that
is needed on a mild day) and the second boiler is then needlessly pulled
in.

--
Tony Bryer, Greentram: 'Software to build on' Melbourne, Australia
www.superbeam.co.uk www.eurobeam.co.uk www.greentram.com

On Fri, 29 Apr 2011 12:14:48 +1000, Tony Bryer wrote:


Yes, that was me. We did it the cheap and cheerful way as a proper
---8---

Thanks Tony, I just wondered if you'd found something ready-rolled at non-
eye-watering price. I'll probably just go the external-thermostat and
bunch of switches, maybe relay if needed, route.


--
John Stumbles -- http://yaph.co.uk

militant pacifist

In article , Tony Bryer
writes
On 28 Apr 2011 22:51:03 GMT Yaph wrote :
Anybody have any links or pointers to controls/controllers for setups
using 2 (or more) boilers to supply larger-than-usual loads? I recall
someone on this list did such a thing for a church he's involved with.

Yes, that was me. We did it the cheap and cheerful way as a proper
sequencer would have cost four figures, not justified, and the ones I
looked at were more suited for a Mon-Fri 8-6 heating regime rather than
the varied times and temps you have with church heating (we had 18C for
services, 19C for longer sitting still meetings, and 15C for flower
arrangers and cleaning).

I've just dug out an old pipework schematic and uploaded it as
http://www.greentram.com/tony/TwinKestonBoiler.pdf

I couldn't see any mention of non return valves in the boiler flows, I'd
have thought they'd be essential for single running.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

On Apr 28, 11:51*pm, YAPH wrote:
Anybody have any links or pointers to controls/controllers for setups
using 2 (or more) boilers to supply larger-than-usual loads? I recall
someone on this list did such a thing for a church he's involved with.
I'm looking at an installation which has a couple of Baxi Solo 2s but no
integration (just a user-unfriendly array of switches and valves to
operate to bring one or both into service as required).

I'm inclined to just have one boiler on load all the time and an outside
thermostat to bring the second in during cold weather (sort of weather
compensation scheme) but it would be interesting to know what's available
(and how much it would cost) to do the job 'properly'.

--
John Stumbles *-- *http://yaph.co.uk

I'd rather have a full bottle in front of me
Than a full-frontal lobotomy

If both boilers are fan flues there isn't going to be a significant
heat loss via the idle unit. I'd be incliined to simply parallel the
two (might need a relay in the call for heat circuitry depending on
the boiler innards) and set one boiler thermostat higher than the
other so it does the majority of the work. Not perfect but simple.

On Fri, 29 Apr 2011 11:21:02 +0100 Fred wrote :
I couldn't see any mention of non return valves in the boiler flows,
I'd have thought they'd be essential for single running.

In theory you need them to stop reverse circulation, but the resistance
of the 1.5m 42mm shunt pipe (aka low loss header) is next to nothing
compared with the 22mm pipes back to the other boiler, its internal pump
and its heat exchanger.

--
Tony Bryer, Greentram: 'Software to build on' Melbourne, Australia
www.superbeam.co.uk www.eurobeam.co.uk www.greentram.com

On Fri, 29 Apr 2011 03:52:16 -0700 (PDT) Cynic wrote :
I'd be incliined to simply parallel the
two (might need a relay in the call for heat circuitry depending on
the boiler innards) and set one boiler thermostat higher than the
other so it does the majority of the work. Not perfect but simple.

That was the Keston suggested method.

--
Tony Bryer, Greentram: 'Software to build on' Melbourne, Australia
www.superbeam.co.uk www.eurobeam.co.uk www.greentram.com

On Fri, 29 Apr 2011 03:52:16 -0700, cynic wrote:

If both boilers are fan flues there isn't going to be a significant heat
loss via the idle unit. I'd be incliined to simply parallel the two
(might need a relay in the call for heat circuitry depending on the
boiler innards) and set one boiler thermostat higher than the other so
it does the majority of the work. Not perfect but simple.

Point. Might just try that first. Though with standard-efficiency boilers
(which is what we have here) where the boiler's thermostatic control
operates on the flow temperature I suspect the one set to the lower
temperature would just cycle on and off, which is not ideal.





--
John Stumbles -- http://yaph.co.uk

I forgot to take my amnesia medecine again

In article , Tony Bryer
writes
On Fri, 29 Apr 2011 11:21:02 +0100 Fred wrote :
I couldn't see any mention of non return valves in the boiler flows,
I'd have thought they'd be essential for single running.

In theory you need them to stop reverse circulation, but the resistance
of the 1.5m 42mm shunt pipe (aka low loss header) is next to nothing
compared with the 22mm pipes back to the other boiler, its internal pump
and its heat exchanger.

Yes, simple is best (less to go wrong) but also, on reflection, flow in
the off boiler would behave just like the flow in the shunt pipe so no
degradation in performance.
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

In article , YAPH
writes
On Fri, 29 Apr 2011 03:52:16 -0700, cynic wrote:

If both boilers are fan flues there isn't going to be a significant heat
loss via the idle unit. I'd be incliined to simply parallel the two
(might need a relay in the call for heat circuitry depending on the
boiler innards) and set one boiler thermostat higher than the other so
it does the majority of the work. Not perfect but simple.

Point. Might just try that first. Though with standard-efficiency boilers
(which is what we have here) where the boiler's thermostatic control
operates on the flow temperature I suspect the one set to the lower
temperature would just cycle on and off, which is not ideal.

I'd like to think that the second boiler would only be required for fast
warm up and during the coldest period of the year so you could extend
the life of the installation by only running 1 except when absolutely
necessary and periodically swapping which one is the primary if you want
to balance the wear.

Say only have boiler 2 on when the return temp is below a certain level
or in combination with an outdoor temp stat? Simple relay logic control
could manage that.

Watch out for over complexity and maintainability, I am reminded
occasionally of this when kind people ask who would maintain x, y & z if
I got run over by a bus tomorrow. The answer is universally, "I wouldn't
give a f'ck" but you may be more concerned :-).
--
fred
FIVE TV's superbright logo - not the DOG's, it's ********

On 28 Apr 2011 22:51:03 GMT, YAPH wrote:

I'm inclined to just have one boiler on load all the time and an outside
thermostat to bring the second in during cold weather (sort of weather
compensation scheme)

Think you would be better off monitoring the flow and return temps
and fireing both boilers until the difference got less than say 10C
then drop one of the boilers off. The logic can probably be done with
simple series connection of flow/return pipe stats, they might need a
change over switch but fairly sure they all have that.

Back feeding one boiler to the other can be controlled with a 2 port
valve wired in the normal way, call valve valve switch boiler.

I like the system Mr Bryer posted, particulary the switch to set
which boiler is "lead". When one goes phut it's simple to use the
other albeit with reduced capacity on the system.

Finally it might be worth looking at a PLC (Process Logic Controller)
to do the logic and switching rather than hard wired stats and
relays. The heating/HW system here is effecively four stat controlled
zones, but with two pumps (2 zones on each pump) from a single boiler
with pump overrun. It works but the logica isn't perfect, if the pump
overun is active for one zone and another calls for heat the
previously active pump overun doesn't drop out. I could probably add
more relays, it already uses six, but if I'd gone for a PLC it would
have just been a tweak of the porogramming.

--
Cheers
Dave.

On Fri, 29 Apr 2011 13:39:07 +0100, fred wrote:

Say only have boiler 2 on when the return temp is below a certain level
or in combination with an outdoor temp stat? Simple relay logic control
could manage that.

I think we're going round in circles here - I originally muttered that I
was thinking of using an outside stat to determine when to bring the 2nd
boiler in with the 1st!

Watch out for over complexity and maintainability, I am reminded
occasionally of this when kind people ask who would maintain x, y & z if
I got run over by a bus tomorrow. The answer is universally, "I wouldn't
give a f'ck" but you may be more concerned :-).

Indeed. That's rather the situation I'm in now: seems whoever designed
(or perhaps "designed") the original system didn't leave (or have :-))
much clue as to how it was supposed to work so I'm trying to work that
out now from what I can see.

--
John Stumbles -- http://yaph.co.uk

Men are from Mars, Women are from Venus and Pop Psychologists are from
Uranus

In message , YAPH
writes
On Fri, 29 Apr 2011 13:39:07 +0100, fred wrote:

Say only have boiler 2 on when the return temp is below a certain level
or in combination with an outdoor temp stat? Simple relay logic control
could manage that.

I think we're going round in circles here - I originally muttered that I
was thinking of using an outside stat to determine when to bring the 2nd
boiler in with the 1st!

Watch out for over complexity and maintainability, I am reminded
occasionally of this when kind people ask who would maintain x, y & z if
I got run over by a bus tomorrow. The answer is universally, "I wouldn't
give a f'ck" but you may be more concerned :-).

Indeed. That's rather the situation I'm in now: seems whoever designed
(or perhaps "designed") the original system didn't leave (or have :-))
much clue as to how it was supposed to work so I'm trying to work that
out now from what I can see.


Have you been "Driveled" ?

--
geoff

On Fri, 29 Apr 2011 22:40:45 +0100, geoff wrote:

Have you been "Driveled" ?

Eagerly waiting to be told to rip it all out and replace with
$FLAVOUR_OF_MONTH :-)



--
John Stumbles

I'd rather have a full bottle in front of me
Than a full-frontal lobotomy

On Fri, 29 Apr 2011 13:45:43 +0100, Dave Liquorice wrote:

On 28 Apr 2011 22:51:03 GMT, YAPH wrote:

I'm inclined to just have one boiler on load all the time and an
outside thermostat to bring the second in during cold weather (sort of
weather compensation scheme)

Think you would be better off monitoring the flow and return temps and
fireing both boilers until the difference got less than say 10C then
drop one of the boilers off. The logic can probably be done with simple
series connection of flow/return pipe stats, they might need a change
over switch but fairly sure they all have that.

Back feeding one boiler to the other can be controlled with a 2 port
valve wired in the normal way, call valve valve switch boiler.

I like the system Mr Bryer posted, particulary the switch to set which
boiler is "lead". When one goes phut it's simple to use the other albeit
with reduced capacity on the system.

Finally it might be worth looking at a PLC (Process Logic Controller) to
do the logic and switching rather than hard wired stats and relays. The
heating/HW system here is effecively four stat controlled zones, but
with two pumps (2 zones on each pump) from a single boiler with pump
overrun. It works but the logica isn't perfect, if the pump overun is
active for one zone and another calls for heat the previously active
pump overun doesn't drop out. I could probably add more relays, it
already uses six, but if I'd gone for a PLC it would have just been a
tweak of the porogramming.


You could use an "intelligent relay" here. You can get them with 4 n.o.
mains-rated contacts and 6 or 8 digital inputs. They include built-in
time switching, timers, logic etc. unfortunately the programming software
and lead is usually charged for, but not as much as for a proper PLC!
Most manufacturers do their own flavour of these. Have a look at the
Crouzet Millenium 3 range. This is a complete kit:
http://uk.rs-online.com/web/search/s...seAction.html?
method=getProduct&R=5368979

Of course, a real tech-head would build a board with a PIC and relays on
it and program it using LDmicro ladder logic for free! http://cq.cx/
ladder.pl


--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Sat, 30 Apr 2011 15:37:40 +0000, mick wrote:

You could use an "intelligent relay" here. You can get them with 4 n.o.
mains-rated contacts and 6 or 8 digital inputs. They include built-in
time switching, timers, logic etc. unfortunately the programming
software and lead is usually charged for, but not as much as for a
proper PLC! Most manufacturers do their own flavour of these. Have a
look at the Crouzet Millenium 3 range. This is a complete kit:
http://uk.rs-online.com/web/search/s...seAction.html?
method=getProduct&R=5368979

Interesting. Probably overkill for this application but not enough for
something like the wood-burner + boiler controller I built recently which
more than half a dozen outputs to pumps & motorised valves.

Presumably the programming s/w is proprietary, closed-source and windoze-
only?

Of course, a real tech-head would build a board with a PIC and relays on
it and program it using LDmicro ladder logic for free! http://cq.cx/
ladder.pl

I thought Arduinos were current flavour of the month? :-)

But even if I were au fait with stuff like that it wouldn't be doing any
favours to my clients, who would have to find someone else to maintain
the system if I got run over by a bus.





--
John Stumbles -- http://yaph.co.uk

DEATH TO FANATICS!

On Apr 30, 9:03*pm, YAPH wrote:
On Sat, 30 Apr 2011 15:37:40 +0000, mick wrote:
You could use an "intelligent relay" here. You can get them with 4 n.o.
mains-rated contacts and 6 or 8 digital inputs. They include built-in
time switching, timers, logic etc. unfortunately the programming
software and lead is usually charged for, but not as much as for a
proper PLC! Most manufacturers do their own flavour of these. Have a
look at the Crouzet Millenium 3 range. This is a complete kit:
http://uk.rs-online.com/web/search/s...seAction.html?
method=getProduct&R=5368979

Interesting. Probably overkill for this application but not enough for
something like the wood-burner + boiler controller I built recently which
more than half a dozen outputs to pumps & motorised valves.

Presumably the programming s/w is proprietary, closed-source and windoze-
only?

Of course, a real tech-head would build a board with a PIC and relays on
it and program it using LDmicro ladder logic for free! *http://cq.cx/
ladder.pl

I thought Arduinos were current flavour of the month? :-)

But even if I were au fait with stuff like that it wouldn't be doing any
favours to my clients, who would have to find someone else to maintain
the system if I got run over by a bus.

--
John Stumbles *-- *http://yaph.co.uk

DEATH TO FANATICS!

Ahh - wood-burner/CH boiler interface. Two pumps, one motorised valve,
3 relays and some resistor-diode logic. Simples. - that is until you
try plumbing in the Dunsley neutraliser.

Rob

On Apr 30, 9:41*pm, robgraham wrote:
On Apr 30, 9:03*pm, YAPH wrote:









On Sat, 30 Apr 2011 15:37:40 +0000, mick wrote:
You could use an "intelligent relay" here. You can get them with 4 n.o.
mains-rated contacts and 6 or 8 digital inputs. They include built-in
time switching, timers, logic etc. unfortunately the programming
software and lead is usually charged for, but not as much as for a
proper PLC! Most manufacturers do their own flavour of these. Have a
look at the Crouzet Millenium 3 range. This is a complete kit:
http://uk.rs-online.com/web/search/s...seAction.html?
method=getProduct&R=5368979

Interesting. Probably overkill for this application but not enough for
something like the wood-burner + boiler controller I built recently which
more than half a dozen outputs to pumps & motorised valves.

Presumably the programming s/w is proprietary, closed-source and windoze-
only?

Of course, a real tech-head would build a board with a PIC and relays on
it and program it using LDmicro ladder logic for free! *http://cq.cx/
ladder.pl

I thought Arduinos were current flavour of the month? :-)

But even if I were au fait with stuff like that it wouldn't be doing any
favours to my clients, who would have to find someone else to maintain
the system if I got run over by a bus.

--
John Stumbles *-- *http://yaph.co.uk

DEATH TO FANATICS!

Ahh - wood-burner/CH boiler interface. Two pumps, one motorised valve,
3 relays and some resistor-diode logic. *Simples. - that is until you
try plumbing in the Dunsley neutraliser.

Rob

I forgot to add that I have an aquaintance who lives in an ancient
pile and has a two boiler system. I've never asked him how it works,
but he is a microwave engineer and his solution to one piping problem
was to run the return concentric with the feed. I perhaps would
really want to know how the system as a whole works - I saw the boiler
room once and it was like something out of Para Handy's puffer.

Rob

In message m, mick
writes
On Fri, 29 Apr 2011 13:45:43 +0100, Dave Liquorice wrote:

On 28 Apr 2011 22:51:03 GMT, YAPH wrote:

I'm inclined to just have one boiler on load all the time and an
outside thermostat to bring the second in during cold weather (sort of
weather compensation scheme)

Think you would be better off monitoring the flow and return temps and
fireing both boilers until the difference got less than say 10C then
drop one of the boilers off. The logic can probably be done with simple
series connection of flow/return pipe stats, they might need a change
over switch but fairly sure they all have that.

Back feeding one boiler to the other can be controlled with a 2 port
valve wired in the normal way, call valve valve switch boiler.

I like the system Mr Bryer posted, particulary the switch to set which
boiler is "lead". When one goes phut it's simple to use the other albeit
with reduced capacity on the system.

Finally it might be worth looking at a PLC (Process Logic Controller) to
do the logic and switching rather than hard wired stats and relays. The
heating/HW system here is effecively four stat controlled zones, but
with two pumps (2 zones on each pump) from a single boiler with pump
overrun. It works but the logica isn't perfect, if the pump overun is
active for one zone and another calls for heat the previously active
pump overun doesn't drop out. I could probably add more relays, it
already uses six, but if I'd gone for a PLC it would have just been a
tweak of the porogramming.


You could use an "intelligent relay" here. You can get them with 4 n.o.
mains-rated contacts and 6 or 8 digital inputs. They include built-in
time switching, timers, logic etc. unfortunately the programming software
and lead is usually charged for, but not as much as for a proper PLC!
Most manufacturers do their own flavour of these. Have a look at the
Crouzet Millenium 3 range. This is a complete kit:
http://uk.rs-online.com/web/search/s...seAction.html?
method=getProduct&R=5368979

Of course, a real tech-head would build a board with a PIC and relays on
it and program it using LDmicro ladder logic for free! http://cq.cx/
ladder.pl


He couldn't really do "any of the above" could he

AIUI, its in a customer's house and he would be responsible for whatever
he installed

Lets get back to reality


--
geoff

On Sat, 30 Apr 2011 20:03:03 +0000, YAPH wrote:

On Sat, 30 Apr 2011 15:37:40 +0000, mick wrote:

You could use an "intelligent relay" here. You can get them with 4 n.o.
mains-rated contacts and 6 or 8 digital inputs. They include built-in
time switching, timers, logic etc. unfortunately the programming
software and lead is usually charged for, but not as much as for a
proper PLC! Most manufacturers do their own flavour of these. Have a
look at the Crouzet Millenium 3 range. This is a complete kit:
http://uk.rs-online.com/web/search/s...seAction.html?
method=getProduct&R=5368979

Interesting. Probably overkill for this application but not enough for
something like the wood-burner + boiler controller I built recently
which more than half a dozen outputs to pumps & motorised valves.

Presumably the programming s/w is proprietary, closed-source and
windoze- only?



How on earth did you guess? ;-)
I've run the Crouzet demo software in a XP virtual machine under linux,
but not for actual programming (the demo won't do it). It didn't want to
run properly under wine (at the time).


Of course, a real tech-head would build a board with a PIC and relays
on it and program it using LDmicro ladder logic for free!
http://cq.cx/ ladder.pl

I thought Arduinos were current flavour of the month? :-)



Only if you happen to have them. I just happen t have a dozen or so
assorted PICs and a programmer so I don't really feel the urge to invest
in even more junk to clutter the place up.


But even if I were au fait with stuff like that it wouldn't be doing any
favours to my clients, who would have to find someone else to maintain
the system if I got run over by a bus.

Now that can be a problem ...
However, it always is. It doesn't matter what form the logic takes,
someone is going to have to maintain the system - even if it involves
reverse-engineering your work. This is something that I used to get
involved in as a control panel designer!

The most basic, and expensive, system is to use relays and timers. It
costs a bomb but is quite easy to maintain. Design and assembly time is
quite high. Pretty good on systems running off 110vDC tripping batteries
though. Not much else can handle this. Also very good when all signals
are at mains voltage.

PLCs can cost even more and aren't maintainable after about 10 years
anyway (no bits made now mate!). Lithium battery usually supports clock/
calender and, sometimes, user-changeable values. That goes flat in about
10 years and the usr will *not* have changed it regularly you can bet!
Quite often the logic is self-checking, with regular memory tests. PLCs
get *very, very* expensive as soon as someone mentions "analogue i/o".

Intelligent relays have the programmable advantage of PLCs, but with a
lot less cost. The internal lithium battery will run the clock/calender
functions for about 10 years. I suspect that the logic isn't self-
checking. Some can do analogue input & PWM output.

PIC & similar chips are a bit new yet. Very promising, but not self-
checking logic so not good for replacing PLCs where it is critical. Can
be *very* cost-effective though. You can always fit a socket and supply a
few spares too, although if you've got the i/o designed right they'll
probably never be needed. You could even do the whole jobby as a plug-in
module now.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Sat, 30 Apr 2011 23:07:52 +0100, geoff wrote:

snip

He couldn't really do "any of the above" could he

AIUI, its in a customer's house and he would be responsible for whatever
he installed

Lets get back to reality


It doesn't matter what we install in a customer's house - we are
responsible for that installation whether we like it or not! :-) Also,
there's really no reason why a well designed and built little PCB should
be any more unreliable than any other piece of electronics - probably
much more reliable than the boiler's PCB.


OK, reality:
A 2-boiler system will almost always have the boilers connected in
parallel for a start. If they aren't arranged like that then it's 2
separate systems.

YAPH is on the right track with his original post, except that the lag
boiler is usually brought on by a stat in the common return main.
Sometimes you may find that it is locked out by an external stat set at
about 16C, so that the lag burner isn't brought in when the weather picks
up. The 2 burners are usually switched to equalize the wear on them. This
can be done automatically using a step relay or manually (much more
common).

Quite often frost protection will run only the lead boiler, but if the
return main doesn't reach a minimum temperature within a set time the lag
boiler will also fire. If the system already has a frost protection
system as part of the room stat (e.g. night set-back) or other
temperature controller then you can probably ignore this. Don't depend on
just the boiler's frost protection though - that's usually designed to
protect the boiler, not the plumbing. A lot of systems used to use 2-
stage frost frost protection. On air frost (outside stat) the heating
pumps run. That keeps the water in the system moving and less likely to
freeze, as residual heat from the warmer rooms protects the colder pipes.
On low return main temperature the (lead) boiler fires until the low
return main stat is again satisfied.

On bigger boilers you would need back-end valves to isolate them, but on
something this size they aren't needed.

I'm not quite sure how the pump is handled in this application (the
manual says that the pump must be connected to the boiler). It should
probably be controlled by the lead boiler only, so 2 extra switching poles
(on the lead boiler select switch) would be needed.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

In message om, mick
writes
On Sat, 30 Apr 2011 23:07:52 +0100, geoff wrote:

snip

He couldn't really do "any of the above" could he

AIUI, its in a customer's house and he would be responsible for whatever
he installed

Lets get back to reality


It doesn't matter what we install in a customer's house - we are
responsible for that installation whether we like it or not! :-)

Nevertheless, in John's case, unless it's a favour job for a friend, I
think that he should stick to off the shelf solutions

The reality (I like that word) is that if it goes wrong within, say, 12
months, and John, for some reason, illness or whatever, is not in a
position to be able to rectify the fault, he would still be liable for
someone else to come along and rectify the situation

Sometimes, you need to look a bit beyond the tip of your soldering iron

Also,
there's really no reason why a well designed and built little PCB should
be any more unreliable than any other piece of electronics - probably
much more reliable than the boiler's PCB.

I should f'ing well hope so



--
geoff

On Sun, 01 May 2011 11:33:54 +0100, geoff wrote:

In message om, mick
writes
On Sat, 30 Apr 2011 23:07:52 +0100, geoff wrote:

snip

He couldn't really do "any of the above" could he

AIUI, its in a customer's house and he would be responsible for
whatever he installed

Lets get back to reality


It doesn't matter what we install in a customer's house - we are
responsible for that installation whether we like it or not! :-)

Nevertheless, in John's case, unless it's a favour job for a friend, I
think that he should stick to off the shelf solutions


Hokay...

(Assuming that system has a timeswitch and room stat and that no further
frost protection is needed)

Existing: Live to t/sw + room stat instead of feeding directly into SL on
boiler feeds lead boiler signal.

Live from t/sw, before room stat, goes via new return main stat to lag
boiler signal.

Now either specify boiler1 or boiler2 as lead and connect up or arrange
switching (these boilers seem to be operated by a simple switched-live SL
input). If not switched then pump is from whichever is lead boiler.

If switched, a 3-pole 2-way switch would be needed. 2 poles wired as a
reversing switch from lead/lag to boiler1/boiler2 and the 3rd pole
switching the pump live from one boiler to the other to keep it in step
with the lead boiler.

Minimum cost, 1 return main stat. Optional 16C external hold-off stat in
series with it. Optional 3-pole 2-way mains-rated switch for duty select
(must be able to handle the pump load).

Each boiler should have it's own means of isolation, breaking both the
continuous live and the SL connection.


The reality (I like that word) is that if it goes wrong within, say, 12
months, and John, for some reason, illness or whatever, is not in a
position to be able to rectify the fault, he would still be liable for
someone else to come along and rectify the situation

Sometimes, you need to look a bit beyond the tip of your soldering iron


That's a good reason to make the system easy to fix. As I've shown above,
though, in this case you could make this work pretty well without adding
more than a couple of stats and a switch. It's a pretty standard sort of
circuit for dual-boiler heating systems and shouldn't flummox any heating
engineer worth his salt too much. The important thing, above all else, is
to document your work and leave a copy with the customer (who *will* lose
it, but it makes them feel better) and another inside your control box/
panel/whatever. Even electronic solutions can be sorted out then.


Also,
there's really no reason why a well designed and built little PCB should
be any more unreliable than any other piece of electronics - probably
much more reliable than the boiler's PCB.

I should f'ing well hope so

grin yeah ...

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Sun, 01 May 2011 10:11:38 +0000, mick wrote:

It doesn't matter what we install in a customer's house - we are
responsible for that installation whether we like it or not! :-) Also,
there's really no reason why a well designed and built little PCB should
be any more unreliable than any other piece of electronics - probably
much more reliable than the boiler's PCB.

Yebbut there's probability of failure and consequences of failure. The
little PCB may be orders of magnitude more reliable than the alternative
implementation in thermostats and switches and relays and what have you;
however you can replace stats and relays etc off the shelf but when the
PCB goes tits-up[1] you're totally Fukushimaed.

OK, reality:
A 2-boiler system will almost always have the boilers connected in
parallel for a start. If they aren't arranged like that then it's 2
separate systems.

YAPH is on the right track with his original post, except that the lag
boiler is usually brought on by a stat in the common return main.

I did consider that but it means the lag boiler will drop out before the
system's up to full temperature leaving the lead boiler struggling to
achieve a good system temp in the coldest weather, when it's needed most.
It'll also be dependent on the setting of the boiler's own thermostats,
whereas an external stat, once set right, should Just Work.

Sometimes you may find that it is locked out by an external stat set at
about 16C, so that the lag burner isn't brought in when the weather
picks up. The 2 burners are usually switched to equalize the wear on
them. This can be done automatically using a step relay or manually
(much more common).

Thinking to the future, when either of the existing boilers finally keels
over it'll obviously be replaced by a condensing one, but (the customer
being a charity with limited funds) there's no reason to replace both at
the same time. And then it'll be desirable to run the higher-efficiency
one most of the time with the s-e only coming in to help out in colder
weather. So, no automatic switch-over. And, as long as the lag boiler is
tested from time to time to ensure it hasn't quietly died without being
noticed, I don't see much reason to switch between them at all.

Quite often frost protection --8--

Not an issue he the upper floors of the building are residential and
occupied 24*7*52 so there will always be some heating.

I'm not quite sure how the pump is handled in this application (the
manual says that the pump must be connected to the boiler). It should
probably be controlled by the lead boiler only, so 2 extra switching
poles (on the lead boiler select switch) would be needed.

Hah! You should see the system :-)

Each boiler has its own 15/60, and its own auto bypass and feed and vent
connections (to common f&e and vent pipes to the header tank in the
attic). The boilers' returns are commoned, and their flows are too, but
via 2-port Satchwell/Sunvic MOMOs. Which have their heads missing and the
valve body left in the open position (so they're commoned too). Then the
combined flow goes to 2 (count 'em: 2!) 15/50s, paralleled, with
isolation valves and a typescript instruction sheet on the door (in a
glazed frame!) commanding the user to operate one or other pump at a time
(there are ordinary 1g1w light-switches on the wall controlling them)
whilst using the valves to isolate the unused one. (The instructions go
on at length about what switches and valves to operate for winter and
summer operation etc: even I found them difficult to follow and the
reason I was there was because the poor woman who's taken over running
the office and inherited the responsibility for operating the system was
totally baffled by it all!)



[1] and Murphy's been at the spare(s) :-/





--
John Stumbles -- http://yaph.co.uk

I'd give my right arm to be ambidextrous

On Sun, 01 May 2011 13:00:24 +0000, YAPH wrote:

On Sun, 01 May 2011 10:11:38 +0000, mick wrote:

It doesn't matter what we install in a customer's house - we are
responsible for that installation whether we like it or not! :-) Also,
there's really no reason why a well designed and built little PCB
should be any more unreliable than any other piece of electronics -
probably much more reliable than the boiler's PCB.

Yebbut there's probability of failure and consequences of failure. The
little PCB may be orders of magnitude more reliable than the alternative
implementation in thermostats and switches and relays and what have you;
however you can replace stats and relays etc off the shelf but when the
PCB goes tits-up[1] you're totally Fukushimaed.

OK, reality:
A 2-boiler system will almost always have the boilers connected in
parallel for a start. If they aren't arranged like that then it's 2
separate systems.

YAPH is on the right track with his original post, except that the lag
boiler is usually brought on by a stat in the common return main.

I did consider that but it means the lag boiler will drop out before the
system's up to full temperature leaving the lead boiler struggling to
achieve a good system temp in the coldest weather, when it's needed
most. It'll also be dependent on the setting of the boiler's own
thermostats, whereas an external stat, once set right, should Just Work.



The return main stat isn't set very far (say 5-10C) below the flow temp
control stat. That way the lead boiler, although it cycles to keep the
return temp up, isn't actually worked too hard as the lag boiler will
kick in if the extra heat is needed. Of course, both boilers run on a
cold system. An external stat used alone can cause confusion as usually
it will be calling for heat while the room stat is satisfied. As soon as
the room stat calls for heat both boilers will kick in. That's fine if
the room stat has a wide differential, but it's also very uncomfortable
having the temperature oscillating. Far better to reduce the differential
and only use the lead boiler to keep the system "topped up".

snip


I'm not quite sure how the pump is handled in this application (the
manual says that the pump must be connected to the boiler). It should
probably be controlled by the lead boiler only, so 2 extra switching
poles (on the lead boiler select switch) would be needed.

Hah! You should see the system :-)

Each boiler has its own 15/60, and its own auto bypass and feed and vent
connections (to common f&e and vent pipes to the header tank in the
attic). The boilers' returns are commoned, and their flows are too, but
via 2-port Satchwell/Sunvic MOMOs. Which have their heads missing and
the valve body left in the open position (so they're commoned too). Then
the combined flow goes to 2 (count 'em: 2!) 15/50s, paralleled, with
isolation valves and a typescript instruction sheet on the door (in a
glazed frame!) commanding the user to operate one or other pump at a
time (there are ordinary 1g1w light-switches on the wall controlling
them) whilst using the valves to isolate the unused one. (The
instructions go on at length about what switches and valves to operate
for winter and summer operation etc: even I found them difficult to
follow and the reason I was there was because the poor woman who's taken
over running the office and inherited the responsibility for operating
the system was totally baffled by it all!)



[1] and Murphy's been at the spare(s) :-/


So if you run both boilers you have paralleled 15/60s pumping through a
single 15/50? Now that's weird! Have the boilers been changed from
something else in the past?

That arrangement of "parallel" pumps is very common in heating systems.
They are quite often put in the return flow though, as the reduced heat
is (or used to be) considered better for the pumps. There is usually a "1-
off-2" switch to control them if there is a control panel, the switch
being used to equalize the wear. With this arrangement you can, of
course, remove a pump for maintenance while the system is running. One of
the valves on each pump is often a non-return valve so that with one pump
running there is no back-flow through the remaining pump. That way you
don't need to valve off the reserve pump.

Believe me, it's a pig trying to write those instructions and produce the
fancy drawings for the glazed frames! I still do those jobs even though I
don't design control panels now.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Sun, 01 May 2011 12:58:03 +0000, mick wrote:

Hokay...

(Assuming that system has a timeswitch and room stat and that no further
frost protection is needed)

Actually 3 zones of CM907/927 progstats and 2-port motorised valves (plus
HW zone) but yeah ...

Existing: Live to t/sw + room stat instead of feeding directly into SL
on boiler feeds lead boiler signal.

Live from t/sw, before room stat, goes via new return main stat to lag
boiler signal.

Why? That would bring the lag boiler on when there's no call for heat.

Now either specify boiler1 or boiler2 as lead and connect up or arrange
switching (these boilers seem to be operated by a simple switched-live
SL input). If not switched then pump is from whichever is lead boiler.

If switched, a 3-pole 2-way switch would be needed. 2 poles wired as a
reversing switch from lead/lag to boiler1/boiler2 and the 3rd pole
switching the pump live from one boiler to the other to keep it in step
with the lead boiler.

Since the boiler each has its own pump only 2g2w switch required -
standard-ish from elec wholesalers.

With external thermostat it would be simple enough: call-for heat (output
of zone valves combined) goes direct to lead boiler's SL, and via
external 'stat to lag boiler's SL (with the changeover switch swapping
over the connections).

Minimum cost, 1 return main stat. Optional 16C external hold-off stat in
series with it. Optional 3-pole 2-way mains-rated switch for duty select
(must be able to handle the pump load).

Each boiler should have it's own means of isolation, breaking both the
continuous live and the SL connection.

Yup, fan isolation switch to each.


That's a good reason to make the system easy to fix. As I've shown
above, though, in this case you could make this work pretty well without
adding more than a couple of stats and a switch. It's a pretty standard
sort of circuit for dual-boiler heating systems and shouldn't flummox
any heating engineer worth his salt too much. The important thing, above
all else, is to document your work and leave a copy with the customer
(who *will* lose it, but it makes them feel better) and another inside
your control box/ panel/whatever.

Heh, yes - preferable glued in!


--
John Stumbles -- http://yaph.co.uk

Teenagers: tired of being harassed by your stupid parents? Act now! -
Move out, get a job and pay your own bills, while you still know
everything!

On Sun, 01 May 2011 12:58:03 +0000, mick wrote:

Hokay...

(Assuming that system has a timeswitch and room stat and that no further
frost protection is needed)

Actually 3 zones of CM907/927 progstats and 2-port motorised valves (plus
HW zone) but yeah ...

Existing: Live to t/sw + room stat instead of feeding directly into SL
on boiler feeds lead boiler signal.

Live from t/sw, before room stat, goes via new return main stat to lag
boiler signal.

Why? That would bring the lag boiler on when there's no call for heat.

Now either specify boiler1 or boiler2 as lead and connect up or arrange
switching (these boilers seem to be operated by a simple switched-live
SL input). If not switched then pump is from whichever is lead boiler.

If switched, a 3-pole 2-way switch would be needed. 2 poles wired as a
reversing switch from lead/lag to boiler1/boiler2 and the 3rd pole
switching the pump live from one boiler to the other to keep it in step
with the lead boiler.

Since the boiler each has its own pump only 2g2w switch required -
standard-ish from elec wholesalers.

With external thermostat it would be simple enough: call-for heat (output
of zone valves combined) goes direct to lead boiler's SL, and via
external 'stat to lag boiler's SL (with the changeover switch swapping
over the connections).

Minimum cost, 1 return main stat. Optional 16C external hold-off stat in
series with it. Optional 3-pole 2-way mains-rated switch for duty select
(must be able to handle the pump load).

Each boiler should have it's own means of isolation, breaking both the
continuous live and the SL connection.

Yup, fan isolation switch to each.


That's a good reason to make the system easy to fix. As I've shown
above, though, in this case you could make this work pretty well without
adding more than a couple of stats and a switch. It's a pretty standard
sort of circuit for dual-boiler heating systems and shouldn't flummox
any heating engineer worth his salt too much. The important thing, above
all else, is to document your work and leave a copy with the customer
(who *will* lose it, but it makes them feel better) and another inside
your control box/ panel/whatever.

Heh, yes - preferable glued in!


--
John Stumbles -- http://yaph.co.uk

Teenagers: tired of being harassed by your stupid parents? Act now! -
Move out, get a job and pay your own bills, while you still know
everything!

On Sun, 01 May 2011 13:55:39 +0000, YAPH wrote:

On Sun, 01 May 2011 12:58:03 +0000, mick wrote:

Hokay...

(Assuming that system has a timeswitch and room stat and that no
further frost protection is needed)

Actually 3 zones of CM907/927 progstats and 2-port motorised valves
(plus HW zone) but yeah ...

Existing: Live to t/sw + room stat instead of feeding directly into SL
on boiler feeds lead boiler signal.

Live from t/sw, before room stat, goes via new return main stat to lag
boiler signal.

Why? That would bring the lag boiler on when there's no call for heat.



Oops! Yeah - sorry. After T/sw + room stat.


Now either specify boiler1 or boiler2 as lead and connect up or arrange
switching (these boilers seem to be operated by a simple switched-live
SL input). If not switched then pump is from whichever is lead boiler.

If switched, a 3-pole 2-way switch would be needed. 2 poles wired as a
reversing switch from lead/lag to boiler1/boiler2 and the 3rd pole
switching the pump live from one boiler to the other to keep it in step
with the lead boiler.

Since the boiler each has its own pump only 2g2w switch required -
standard-ish from elec wholesalers.

With external thermostat it would be simple enough: call-for heat
(output of zone valves combined) goes direct to lead boiler's SL, and
via external 'stat to lag boiler's SL (with the changeover switch
swapping over the connections).



Personally, I wouldn't be happy with just an external stat for lag boiler
control but YMMV. IMHO the vagaries of the English climate would leave
you twiddling that stat until doomsday trying to get it "just right".


Minimum cost, 1 return main stat. Optional 16C external hold-off stat
in series with it. Optional 3-pole 2-way mains-rated switch for duty
select (must be able to handle the pump load).

Each boiler should have it's own means of isolation, breaking both the
continuous live and the SL connection.

Yup, fan isolation switch to each.


That's a good reason to make the system easy to fix. As I've shown
above, though, in this case you could make this work pretty well
without adding more than a couple of stats and a switch. It's a pretty
standard sort of circuit for dual-boiler heating systems and shouldn't
flummox any heating engineer worth his salt too much. The important
thing, above all else, is to document your work and leave a copy with
the customer (who *will* lose it, but it makes them feel better) and
another inside your control box/ panel/whatever.

Heh, yes - preferable glued in!

Wouldn't be the first time that's been done either! (by me ...)


The pumps still have me confused. The 15/60 can handle a greater head
than the 15/50 so why were the external 15/50 pumps fitted? Is the head
still too much for the internal 15/60s alone, and they were added to give
them a bit of help I wonder? I could understand that if it was
anticipated that only one boiler would run at once. I'm not a heating
engineer, perhaps someone else can help? I suspect that the 15/50s will
be set for full flow and the 15/60s throttled back to give about 1/2 the
15/50s flow each. Only a guess.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Sun, 01 May 2011 13:55:39 +0000, YAPH wrote:

snip

Since the boiler each has its own pump only 2g2w switch required -
standard-ish from elec wholesalers.

snip


Ah... yes... those pumps.

I've just been a-googling and come up with this:
http://www.engineeringtoolbox.com/pu...ial-d_636.html
"Centrifugal pump in series are used to overcome larger system head loss
than one pump can handle alone. For two identical pumps in serie the head
will be twice the head of a single pump at the same flow rate."
"Series operation of single stage pumps is seldom encountered - more
often multistage centrifugal pumps are used."

But:
http://www.mcnallyinstitute.com/05-html/5-12.html
"If you connect the pumps in series, the heads will add together, so the
capacities must be the same or one of them will probably cavitate. You
could also have a problem operating too far to the right of the best
efficiency point with a possible motor "burn out"."


IMHO if the system is currently working ok with either one or both
boilers running (without the noise of pump cavitation) then you should be
ok as you are only changing the control method. However, if the system
doesn't currently run like this (e.g. only one boiler runs at once) then
I should be tempted to leave well alone for the moment. There may well be
a way around this but I'm not qualified to answer.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Sun, 01 May 2011 14:28:01 +0000, mick wrote:

The pumps still have me confused. The 15/60 can handle a greater head
than the 15/50 so why were the external 15/50 pumps fitted? Is the head
still too much for the internal 15/60s alone, and they were added to
give them a bit of help I wonder? I could understand that if it was
anticipated that only one boiler would run at once. I'm not a heating
engineer, perhaps someone else can help? I suspect that the 15/50s will
be set for full flow and the 15/60s throttled back to give about 1/2 the
15/50s flow each. Only a guess.

I haven't done the mass/flow calculations (and it would be hard to, given
that I don't know where half the pipework goes) but it's basically a
large-ish house with several parallel circuits, some of them single-pipe,
which shouldn't be wildly demanding for a 15/60. If anything I guess it
would want more flow than head - more like the 2 15/50s paralleled,
except that the original installers instructions are to use only one of
these at a time. (There's no reason you *couldn't* use both together, but
the instructions suggest it wasn't designed to be used that way.) So, a
mystery.

I'll probably take out the two paralleled pumps and see how it goes with
the 15/60s fitted to the boilers, and have a re-think if that doesn't
play nicely.


--
John Stumbles -- http://yaph.co.uk

Bad artists borrow
Great artists steal
Igor Stravinsky

In message , YAPH
writes
So if you run both boilers you have paralleled 15/60s pumping through a
single 15/50? Now that's weird! Have the boilers been changed from
something else in the past?

The boilers may well have been changed: the rads are non-finned types but
the boilers are Baxi Solo 2s so they're newer than the original
installation I'd guess. Even so it would be odd if they'd fitted new
boilers with extra pumps and not removed the pair of 15/50s.


Don't forget that there is an 8-10min pump overrun from each pcb


--
geoff

On Mon, 02 May 2011 22:28:09 +0000, YAPH wrote:

On Sun, 01 May 2011 14:28:01 +0000, mick wrote:

The pumps still have me confused. The 15/60 can handle a greater head
than the 15/50 so why were the external 15/50 pumps fitted? Is the head
still too much for the internal 15/60s alone, and they were added to
give them a bit of help I wonder? I could understand that if it was
anticipated that only one boiler would run at once. I'm not a heating
engineer, perhaps someone else can help? I suspect that the 15/50s will
be set for full flow and the 15/60s throttled back to give about 1/2
the 15/50s flow each. Only a guess.

I haven't done the mass/flow calculations (and it would be hard to,
given that I don't know where half the pipework goes) but it's basically
a large-ish house with several parallel circuits, some of them
single-pipe, which shouldn't be wildly demanding for a 15/60. If
anything I guess it would want more flow than head - more like the 2
15/50s paralleled, except that the original installers instructions are
to use only one of these at a time. (There's no reason you *couldn't*
use both together, but the instructions suggest it wasn't designed to be
used that way.) So, a mystery.

I'll probably take out the two paralleled pumps and see how it goes with
the 15/60s fitted to the boilers, and have a re-think if that doesn't
play nicely.



I was going to suggest that, but I thought you may not want to be messing
with the plumbing! I can't see why they would be needed. You parallel
pumps to get more flow and series them to get more head capability. Even
putting a 15/50 in series with a 15/60 won't get you the full sum of
their heads though, so there wouldn't be much to gain IMHO.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Tue, 03 May 2011 08:58:52 +0000, mick wrote:

On Mon, 02 May 2011 22:17:28 +0000, YAPH wrote:

Seems to me the lag boiler should only fire when there's call for heat
from any of the zones AND the outside temperature's below the external
'stat set point.


Yep, it will work, but not ideally.

If the weather is very cold it acts like a single big boiler, that's
fine.

If the weather is a bit warmer you will still always fire both boilers

Hmmm. There will be a temperature where it's still cold enough that the
external stat is closed so both boilers get called, but the heat load is
much less that can be supplied by both boilers. The system will heat up
very quickly, and the boilers will cycle, and their anti-cycling
mechanism may kick in. But I don't see that it's different to the
situation in a smaller, conventional one-boiler system in warmer weather
where the load is a lot less than the boiler output: you'll get cycling,
and anti-cycling behaviour, in that situation too, n'est-ce-pas?


I suppose a single "summer-winter switch in series with the external
stat might be ok?

Well that's what the external stat is supposed to be - a summer/winter
switch. But one that takes account of the actual temperature rather than
what the calendar says!


--
John Stumbles -- http://yaph.co.uk

I used to be forgetful but now I ... um ....

On Mon, 02 May 2011 23:40:10 +0100, geoff wrote:

Don't forget that there is an 8-10min pump overrun from each pcb

That should be OK if I use the pumps associated with each boiler. The 2
parallel external ones seemed to be wired to be on 24*7 (OK, switched
manually on the wall) anyway! And hopefully I can do away with those.

--
John Stumbles -- http://yaph.co.uk

This sig intentionally left blank

On Tue, 03 May 2011 08:22:04 +0000, mick wrote:

I was going to suggest that, but I thought you may not want to be
messing with the plumbing! I can't see why they would be needed. You
parallel pumps to get more flow and series them to get more head
capability. Even putting a 15/50 in series with a 15/60 won't get you
the full sum of their heads though, so there wouldn't be much to gain
IMHO.

No, I don't know what the original installer was on but I really don't
see how the existing arrangement could be necessary. With multiple,
mostly single-pipe, circuits in parallel then, if you did need extra
pumps you'd want to add them in parallel to cope with the flow not series
to boost head.





--
John Stumbles -- http://yaph.co.uk

Press any key to continue or any other key to exit

On Tue, 03 May 2011 11:43:10 +0000, YAPH wrote:

On Tue, 03 May 2011 08:58:52 +0000, mick wrote:

On Mon, 02 May 2011 22:17:28 +0000, YAPH wrote:

Seems to me the lag boiler should only fire when there's call for heat
from any of the zones AND the outside temperature's below the external
'stat set point.


Yep, it will work, but not ideally.

If the weather is very cold it acts like a single big boiler, that's
fine.

If the weather is a bit warmer you will still always fire both boilers

Hmmm. There will be a temperature where it's still cold enough that the
external stat is closed so both boilers get called, but the heat load is
much less that can be supplied by both boilers. The system will heat up
very quickly, and the boilers will cycle, and their anti-cycling
mechanism may kick in. But I don't see that it's different to the
situation in a smaller, conventional one-boiler system in warmer weather
where the load is a lot less than the boiler output: you'll get cycling,
and anti-cycling behaviour, in that situation too, n'est-ce-pas?




In theory the anti-cycling protection won't usually kick in much if the
boiler is correctly rated for the load. It will do, but not often. In
multiple boiler systems the effective boiler rating is, of course,
changed by setting the number of boilers available to run. That is
usually done "on the fly" by sensing the return main temperature as I've
said before. That's done with either multiple return main stats
(sometimes with delay timers) or a temperature sensor feeding a boiler
sequencer box. Systems with 2, 3 or even 4 boilers are not uncommon.

In your case, using an outside stat, you *may* have problems. Not
necessarily, because all heating systems vary. It will depend on your
heating load, the response speed of the heating loop, hysteresis of the
system etc. etc.

Your external stat position will be important. An external stat on a
south-facing wall is always useless (artificially warm). The same stat in
the centre of a north-facing wall (not above a window) will work
perfectly. The same stat moved to an external corner of the same north-
facing wall may work well for half the year, depending on the prevailing
winds. The one thing that you do know for certain is that the return main
temperature is always related to the heat loss of the building. If it's
lower than expected then you need more heat input.


I suppose a single "summer-winter switch in series with the external
stat might be ok?

Well that's what the external stat is supposed to be - a summer/winter
switch. But one that takes account of the actual temperature rather than
what the calendar says!


Try it. A single external stat is cheap enough and could still be used if
you later decide to try a return main stat. If you want to try a "summer/
winter" select then just switch off the lag boiler.

And don't trust the weather ... ;-)

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Tue, 03 May 2011 13:33:49 +0000, mick wrote:

In your case, using an outside stat, you *may* have problems. Not
necessarily, because all heating systems vary. It will depend on your
heating load, the response speed of the heating loop, hysteresis of the
system etc. etc.

---8---

Try it. A single external stat is cheap enough and could still be used
if you later decide to try a return main stat. If you want to try a
"summer/ winter" select then just switch off the lag boiler.

Yup, that's my thinking. Start simple, if that's not good enough then's
time for plan B. They're only down the road from me and nice enough
folks, I think they'd understand if it takes a bit of iteration to sort
out what they already know is a weird system.

Only snag I see with my plan A is I should probably arrange to only fire
one boiler when there's only HW demand even when it's cold outside
otherwise I'm pretty much guaranteed cycling. But that's probably not
straightforward electrically. Dammit, now it's getting complicated again!


--
John Stumbles -- http://yaph.co.uk

An atheist is a person with no invisible means of support

I haven't read all this, so excuse me if I repeat an earlier post.
What order of cost do you think would be reasonable for such a a 2
boiler control system? I'm not selling, just interested.

Some boiler manufacturers do controllers for multiple boilers, so that
would be my first port of call.

The usual control system (in BMS systems) is a temperature sensor in
the flow connected to a proportional (or proportional & integral)
controller, with the lead & lag boilers set to operate at various
percentage outputs.

The first boiler control system I came across was a proportional
(output = gain x error) controller (Satchwell Monotronic) which put a
0-10V output into a valve actuator. There were microswitches operated
by the actuator at various points and these operated the 3 boilers' hi/
lo fire burners. The gain and set point was set by pots on the
controller. The disadvantage of proportional controllers was that
there must always be an error from the setpoint to get an output.

When electronics got cheaper, this was replaced by BMS outstations
which could not only control the burner but do all manner of clever
stuff besides (automatic changeover of boilers, duty sharing, high/low
temperature alarms, data logging, frost protection, etc., etc.,). BMS
systems cost an arm and both legs and the programming is intentionally
made inaccessible to non-trade users. There are some cheaper systems
now (see adverts in BSEE magazine) so I'd try there too.

I have some 20 year old BMS outstations that could do this once
programmed; it is tragic that such technology has been made
unavailable to domestic users bt the UK building controls cartel.

On Fri, 06 May 2011 22:25:28 +0000, mick wrote:

Nice. I used some a while ago. They were pretty expensive IIRC. We
changed to some much cheaper 230vAC LED indicators. They are rather
neat, with 2 strings of LEDs so you can still see them if a string has
failed.

I don't think they were horrendously expensive (or I wouldn't have bought
them!) - couple of quid maybe? From CPC.


We used to use tranilamps ages ago, when they were still affordable and
you could get bulbs!

What are/were tranilamps?


--
John Stumbles -- http://yaph.co.uk

Thesaurus: extinct reptile noted for its wide vocabulary.